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Nitrogen-Doped Carbon Nanotube Arrays Perform Better Than Platinum as Fuel Cell Catalysts

6 February 2009

Gong2
CO-poison effect on the i-t chronoamperometric response for Pt-C/GC and VA-NCNT/GC electrodes. The arrow indicates the addition of 55 mL/min CO gas into the 550 mL/min O2 flow. The mixture gas of ~9% CO (volume/volume) was then introduced into the electrochemical cell. From Gong et al. (2009) Click to enlarge.

A team of researchers led by Liming Dai at the University of Dayton, Ohio, has found that arrays of vertically aligned nitrogen-containing carbon nanotubes (VA-NCNTs) can act as a metal-free electrode with a much better electrocatalytic activity, long-term operation stability, insensitivity to CO poisoning and tolerance to crossover effect than platinum for oxygen reduction in alkaline fuel cells.

The ability to replace costly platinum with a much lower-cost carbon-based catalyst could lead to more efficient fuel cells that can be affordably mass-produced. A paper on the findings was published in the 6 Feb issue of the journal Science.

Traditionally, fuel cells employ expensive platinum-based electrocatalysts, which cost about $4,000 for a passenger car. The goal is to reduce the major cost of a fuel cell in order to compete with current market technologies, including gasoline engines. Our finding is a major breakthrough toward commercialization of fuel cell technology for various applications.

—Liming Dai

The oxygen reduction reaction (ORR) at the fuel cell cathode, which breaks apart the O2 molecule, is enabled by the ORR electrocatalyst material and is a key determinant in the performance of the fuel cell. Platinum has been the conventional choice since fuel cells were developed for the Apollo mission in the 1960s, the authors note, but large scale commercial application has been hampered by the high cost of the metal, its susceptibility to time-dependent drift, and to deactivation by CO. Consequently, a great deal of research has gone into reducing the amount of Pt used, or replacing it with a variety of different materials.

The Dai group found that their VA-NCNTs could catalyze a four-electron ORR process with a much higher electrocatalytic, lower overpotential (the difference between thermodynamic and formal potentials), smaller crossover effect, and better long-term operation stability than that of commercially available or similar platinum-based electrodes in alkaline electrolytes.

In air-saturated 0.1 molar potassium hydroxide, we observed a steady-state output potential of –80 millivolts and a current density of 4.1 milliamps per square centimeter at –0.22 volts, compared with –85 millivolts and 1.1 milliamps per square centimeter at –0.20 volts for a platinum-carbon electrode. The incorporation of electron-accepting nitrogen atoms in the conjugated nanotube carbon plane appears to impart a relatively high positive charge density on adjacent carbon atoms. This effect, coupled with aligning the NCNTs, provides a four-electron pathway for the ORR on VA-NCNTs with a superb performance.

—Gong et al. (2009)

The role of nitrogen-doping as shown in this study could be applied to the design and development of various other metal-free efficient ORR catalysts, and these nitrogen-containing carbon nanotube electrodes are clearly of practical importance, the authors note.

Michael Durstock in the Air Force Research Laboratory’s Materials and Manufacturing Directorate; Zhenhai Xia in the University of Akron department of mechanical engineering; and Kuanping Gong and Feng Du in the University of Dayton departments of chemical and materials engineering contributed to the report.

Resources

  • Kuanping Gong et al. (2009) Nitrogen-Doped Carbon Nanotube Arrays with High Electrocatalytic Activity for Oxygen Reduction. Science Vol. 323. no. 5915, p. 753 doi: 10.1126/science.1166510

February 6, 2009 in Catalysts, Fuel Cells, Nanotech | Permalink | Comments (6) | TrackBack (0)

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Comments

Now all we need is low cost high capacity storage, and a cheap source of hydrogen. Simple.

Already got the cheap source or didnt you read the other report here.. They got the cost of h2 down from 5 bucks to 3 bucks a kilo..

A couple of questions:

It doesn't seem like this is quite as power dense as the other "non-platinum" announcement made a day earlier on GCC, but then that's looking at square centimeters. Neither article talks about how thin sheets could be and how densely they could be stacked. With the carbon-nanotube approach, I'd have to assume pretty dang thin/tightly stacked which might yeild a better total volume than the liquid catalyst mentioned in the other article???

Second: this article mentions specifically that it's more resistant to CO problems than platinum. Does that mean it could be used in a direct type fuel cell using methanol or ethanol as it's source of hydgroden or am I mis-understanding something here.

I guess I'm curious about the second question because I know they had some really good work on Direct Methanol Fuel Cells out of JPL a few years ago and it seems to have disappeared because someone got some patents on it that haven't expired yet. That sounds like another conspiracy theory, but a couple of friends of mine who were doing some of the work gave up on it because of that. I was wondering if anyone else had more info and why that approach is no longer being pursued heavily.
It just seems like a lot easier way to deal with the hydrogen issues to me if you could use methanol/ethanol/butanol in a direct fuel cell. And I saw some announcement about an ethanol fuel cell a few weeks ago that I can't find again now.

Th report forgot to mention one small but important detail. There isn't enough platinum on planet earth for all vehicle fuel cells should the Chinese start building cars for their growing middle class.

So... I apologize for my relative ignorance regarding fuel cells. Most of my research has been done in the area of hydrogen fuel cells, however I have read a couple articles about natural gas fuel cells in Japan.

Is the energy density for these other fuel cells better? Are they cheaper per btu?

The fuel cells used in the japan thingies are solid oxide fuel cells and they are used in that system because they want heat and power not just power. A 1 kw sofc stack can heat all your water and some of your home as well while cutting utility bills by a large margin. They are only 35% eff making power but in a combined heat and power app they are nearer 75% or so.

Meanwhile the pem fuel cell car and mobile thingy makers are looking at makes about 40-60% eff power and some heat. But that heat is wasted in the car unless your catching it to heat the car that is;/

solid oxide fuel cells run HOT and need to be hot to run but they also can run directly on natural gas and some other fuels instead of just h2.

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